ANALYSIS OF LIGAND–RECEPTOR INTERACTIONS IN CELLS BY ATOMIC FORCE MICROSCOPY

ABSTRACT

Atomic force microscopy (AFM) increasingly has been used to analyse “receptor” function, either by using purified proteins (“molecular recognition microscopy”) or, more recently, in situ in living cells. The latter approach has been enabled by the use of a modified commercial AFM, linked to a confocal microscope, which has allowed adhesion forces between ligands and receptors in cells to be measured and mapped, and downstream cellular responses analysed. We review the application of AFM to cell biology and, in particular, to the study of ligand–receptor interactions and draw examples from our own work and that of others to show the utility of AFM, including for the exploration of cell surface functionalities. We also identify shortcomings of AFM in comparison to “standard” methods, such as receptor auto-radiography or immuno-detection, that are widely applied in cell biology and pharmacological analysis.     

THE RELEVANT USE OF THE TRADITIONAL TUNISIAN GAME ‘‘RAQASSA’’ FOR CARDIOVASCULAR STIMULATION IN SCHOOLCHILDREN

The aim of this study was to investigate the heart rate (HR) responses, the rate of perceived exertion (RPE), and the feeling during physical education schooling while performing traditional games activities compared to intermittent exercise. Nineteen pre-pubertal children randomly performed on different days two types of lessons (intermittent running mode vs. traditional Tunisian “Raqassa” game) lasting 12-min each. HR was continuously recorded during both lessons, while ratings of perceived exertion and Feeling values were recorded after the sessions. The mean HR value during the traditional game was significantly higher than during intermittent exercise (p<0.05). Conversely, the perceived exertion score was significantly higher after intermittent exercise than the traditional exercise game (p<0.05), showing that the higher cardiovascular strain of the game was perceived as “lighter” than the run. Simultaneously, the children''s Feeling was significantly higher after the traditional game than intermittent exercise (p<0.001), showing a higher satisfaction from playing with respect to running. Exercise based on the “Raqassa” traditional game could be used in pre-pubertal children as an alternative or as an additional method for suitable cardiovascular stimulation during physical education lessons with lower perceived exertion and better feeling compared to intermittent running.     

APPLICATION OF NONLINEAR FORECASTING METHOD TO ANALYSIS OF ISI IN NERVOUS SYSTEM

ＡＰＰＬＩＣＡＴＩＯＮＯＦＮＯＮＬＩＮＥＡＲＦＯＲＥＣＡＳＴＩＮＧＭＥＴＨＯＤＴＯＡＮＡＬＹＳＩＳＯＦＩＳＩＩＮＮＥＲＶＯＵＳＳＹＳＴＥＭＧｏｎｇＹｕｎｆａｎ（龚云帆）ＸｕＪｉａｎｘｕｅ（徐健学）（ＤｅｐａｒｔｍｅｎｔｏｆＥｎｇｉｎｅｅｒｉｎｇＭｅｃ...     

INCOMPATIBILITY IN ABUTILON ‘HYBRIDUM’

Pandey , K. K. (John Innes Hort. Inst., Bayfordbury, Hertford, Herts, England.) Incompatibility in Abutilon ‘Hybridum.’ Amer. Jour. Bot. 47(10): 877–883. Illus. 1960.—Abutilon ‘Hybridum’ (2n = 16) has a one-locus multiallelic gametophytic (Nicotiana-type) system of self-incompatibility. Five S alleles were distinguished among the 4 plants studied. However, the incompatibility behavior in many crosses is obscured by the modifying effects of a number of other genes non-allelic to the S locus. Since A. ‘Hybridum’ is a cultivar which has arisen through hybridization of 2 or more Abutilon species, it is suggested that the mixed polygenic background of the “species” is not adjusted to the proper functioning of the S gene system. Although most of the plants in the 6 groups studied were highly self-incompatible in the early and mid season, many of them showed pseudo-self-compatibility late in the season. Seed-set in illegitimate crosses also increased late in the season. Colchicine-induced autopolyploidy brought about part or full self-compatibility. After incompatible pollination, pollen germination appeared to be normal but a considerable proportion of the tubes were inhibited in the stigmatic region of the style; tubes which penetrated the style usually burst between ⅕ and ⅓ of the distance from the stigma to the base, a phenomenon not found in any of the other gametophytic-type species yet studied.     

ENDOSYMBIOTIC CALCIFYING BACTERIA: A NEW CUE TO THE ORIGIN OF CALCIFICATION IN METAZOA?

Sponges show the highest diversity of associated bacteria among marine invertebrates. Immunological evidence traces the origin of the sponge bacterial symbioses to the Precambrian era. Hence, sponges appear to be ideally suited for studying the evolutionary origins of prokaryote–metazoan associations. Sponges produce either calcareous or siliceous skeletons, which only coexist in a relict group of demosponges, the sclerosponges. We report here, for the first time, intensive calcification in nonsclerosponge siliceous demosponges. Calcification is mediated by endosymbiotic bacteria (calcibacteria) located in archeocyte‐like sponge cells. These calcibacteria are devoid of bacterial walls and divide within sponge cells until they became surrounded by a calcitic sheet, being subsequently extruded to the sponge subectosomal (subepithelial) zone. Thousands of bacteria‐produced calcitic spherules cover the surface of the host sponges, forming a cortex‐like structure that mimics a rudimentary peripheral skeleton. Calcibacteria are vertically transferred to the sponge larvae during embryogenesis. Calcium detoxification may have generated this symbiotic association, with some additional benefits for the sponges, such as skeletal formation and deterrence from predation. This unique symbiosis holds implications for sponge biology and may advance discussions on the role of bacteria in early biocalcification processes in metazoans.     

A MORPHOLOGICAL AND HISTOLOGICAL STUDY OF THE TOMATO MUTANT ‘CURL’

The dominant tomato mutant ‘Curl’ differs from normal plants in several striking respects including the following: misshapen laminar structures such as leaves, sepals, and petals; stunted petiole and rachis; and persistent growth of blade and stem tissue from the adaxial surface of the rachis. These tissues as well as others which appear morphologically normal show gross histological abnormalities. Also evident in sections of mutant tissue is the appearance of areas containing numerous crystalline inclusions and a lack of bodies showing a stainable starch reaction in palisade and mesophyll of leaves and in endodermis and pith cells of the stem.     

QUANTITATIVE CHANGES IN GIBBERELLIN AND RNA CORRELATED WITH SENESCENCE OF THE SHOOT APEX IN THE ‘ALASKA’ PEA

Senescence of shoot apices of Pisum sativum L. ‘Alaska’ as measured by cessation of stem elongation was delayed by removal of flowers and by treatment with gibberellin A₃ and was hastened by treatment with AMO-1618 (2 isopropyl-4-dimethylamino-5-methylphenyl-1-piperi-dinecarboxylate methyl chloride). Ontogenetic changes in relative endogenous gibberellin levels and in capability of gibberellin biosynthesis in deflowered and control plants were determined indirectly by studying time-course changes in the sensitivity, as indicated by the growth response, of these plants to applied gibberellin and AMO-1618. The results of these experiments suggest that the endogenous gibberellin level varies directly with the growth rate. Analyses of total RNA and protein in shoot tips of deflowered and control plants revealed that the levels of these substances also vary directly with growth rate throughout ontogeny. It is concluded that decreases in endogenous gibberellin, RNA and protein are factors correlated with senescence of the shoot apex.     

‘HALOPHYTE FILTERS’: THE POTENTIAL OF CONSTRUCTED WETLANDS FOR APPLICATION IN SALINE AQUACULTURE

World consumption of seafood continues to rise, but the seas and oceans are already overexploited. Land-based (saline) aquaculture may offer a sustainable way to meet the growing demand for fish and shellfish. A major problem of aquaculture is nutrient waste, as most of the nutrients added through feed are released into the environment in dissolved form. Wetlands are nature's water purifiers. Constructed wetlands are commonly used to treat contaminated freshwater effluent. Experience with saline systems is more limited. This paper explores the potential of constructed saline wetlands for treating the nutrient-rich discharge from land-based saline aquaculture systems. The primary function of constructed wetlands is water purification, but other ancillary benefits can also be incorporated into treatment wetland designs. Marsh vegetation enhances landscape beauty and plant diversity, and wetlands may offer habitat for fauna and recreational areas. Various approaches can be taken in utilizing plants (halophytes, macro-algae, micro-algae) in the treatment of saline aquaculture effluent. Their strengths and weaknesses are reviewed here, and a conceptual framework is presented that takes into account economic and ecological benefits as well as spatial constraints. Use of the framework is demonstrated for assessing various saline aquaculture systems in the southwestern delta region of the Netherlands.     

DIRECTIONALITY IN THE WHISTLES OF HAWAIIAN SPINNER DOLPHINS (STENELLA LONGIROSTRIS): A SIGNAL FEATURE TO CUE DIRECTION OF MOVEMENT?

Dolphins produce frequency modulated (FM) whistles that are thought to promote the synchrony and coordination of behavior between members of a group. How whistles are used in this regard remains poorly understood. One possibility is that whistles have directionality and thereby convey the orientation and direction of movement of the signaler to nearby listeners. To explore this possibility, whistles from free-ranging Hawaiian spinner dolphins ( Stenella longirostris ) were obtained using a towed, three-hydrophone line array and examined for the presence of directionality. Both the estimated source level and harmonic content of whistles produced by animals traveling with or toward the array were greater than those of animals moving ahead or away from it. In addition, signals produced by animals near the array (within 20 m) were received differently on the three hydrophones spaced 11.5 m apart. These differences were greater than would be expected from transmission loss disparities alone. The results indicate that directivity is present in the transmission pattern of whistles. To infer the form of this directivity, a theoretical whistle beam pattern was established based on the assumption that the dolphin's sound source is approximated by a circular piston transducer (Au 1993). The resulting beam indicates that spinner dolphin whistles become increasingly directional with frequency, especially with respect to harmonics. The orientation-dependent harmonic structure of whistles thus presents a potential cue that listening animals could interpret to infer the direction of movement of signalers. Harmonics are present in the whistles of many dolphin species and may represent an inherent signal design feature that promotes coordination between animals.